A typical gas laser as shown in FIG. 1 has a pair of opposing mirrors 10 aligned to their common optical axis (which mirrors will be hereinafter referred to as optical resonator), a gas laser tube 1 mounted in the optical resonator and containing a gas such as Argon, and an electromagnetic coil 5 for generating a magnetic field through the length of the laser tube 1.
Mounted inside the gas laser tube 1 are a plasma tube 2 having a central hole 2h, and a pair of a cathode electrode 3 and an anode electrode 4 at the opposite sides of the plasma tube. The plasma tube 2 is often divided into a multiplicity of smaller pieces which are coaxially spaced apart along their common center line.
When a current is passed from the anode electrode to the cathode electrode, gas discharge takes place, generating gaseous ions or plasma between them. In order to confine the plasma within the central hole 2h of the plasma tube 2, the electromagnetic coil 5 is impressed with a voltage to generate a magnetic field oriented generally along the center line of the central hole. By means of gas discharge, the ion plasma is continuously stimulated, creating inverted population distribution over laser transition levels and by means of optical resonator, induced laser emission is amplified.
In such gas lasers, a portion of ions accelerated by the impressed electric field between the electrodes bombard the entrance end and the inner wall of the capillary tube, and can erode the entrance end and the wall due to sputtering. Such sputtering, therefore, disadvantageously shorten life of the laser tube.